I'm on my trip to Gulangyu Island, Xiamen, Fujian Province, China. Today(4th February 2017), at 12:13 A.M., I saw a beach filled with huge rocks on which various dry shells reside. Among the shells, I spotted a colorful eye-like marine creature.
To figure out what it is, I torn it off from the rock. (don't worry, I've put it back after taking this photo)
Also, it feels soft when I poked it, and its size is approximately 1cm to 1cm. Could anybody please tell me what I've found?
You've found a sea anemone, a cnidarian of the Order Actiniaria. In this case, the anemone is closed and thus hiding its characteristic tentacles (likely as a form of protection while "out to dry").
I'm by no means an expert, but my guess is that you have a vertically striped species of the genus Diadumene -- likely one of many morphotypes of the species Diadumene lineata. I've seen common names vary between "Striped Sea Anemone", "Lined Bead Anemone" and "Orange-Striped Green Anemone."
Here is a double stripe specimen from San Francisco, and below are two pictures from Ria Tan's Wild Singapore image collection:
Open:
Without further information regarding size, color/length of tentacles etc., it will be hard for a non-expert like me to find a better answer.
According to the Wikipedia page, this species originated along the Pacific coast of Asia, but has spread more globally from attachment to ship bottoms, oyster shipments, and seaweed farming.
It appears from your picture, that you found your specimen out of water along the shoreline. Again according to the Wikipedia article:
Diadumene anemones display high tolerance to inter-tidal exposure and drying out in extreme summer heat
